To prevent environmental pollution from being generated, and accelerate a higher reduction of the volume by obtaining a residue having combustible components of which the volume has been reduced by heat-treating object to be treated, and incinerating the residue by burning, or heat-treating the objects to be treated by mixing or adding a chemical, and burning the residue which has been made harmless.

Objects to be treated containing organic substances are pulverized by crushing, and the pulverized objects are thrown into a rotating cylindrical body 2 through a hopper 14. A residue of which the volume has been reduced by a heat- treatment, and which has combustible components (e.g. carbide) is obtained in the rotating cylindrical body 2. The residue is incinerated by an incineration furnace. When a chemical is used, the objects to be treated and a chemical comprising an alkaline substance are mixed (or added). After sufficiently mixing them, they are thrown into the rotating cylindrical body 2 through the hopper 14, and the objects to be treated are dried, and then, thermally dissolved to deposit harmful components from the objects to be treated, and simultaneously, a reaction with the chemical is performed. Then, after heat-treated in the rotating cylindrical body 2 for a specified period of time, the objects to be treated are discharged from the discharging duct 10.